1. Field of the Invention
The invention relates to a method and apparatus for ascertaining tool path contours approximating curved contour intersection lines by means of numerically controlled machines and particularly to a method of interpolating a curved contour intersection line so that a machine cutting tool path contour approximates the curved contour.
2. Description of the Prior Art
In numerically controlled (NC) machine tools, data is determined for producing a workpiece from a workpiece blank in the form of tool path data by means of an NC program. This requires correcting the contour of the workpiece to be produced with the tool radius, since it is not the workpiece contour but rather the center point of the tool path that is relevant to the machine in producing the workpiece.
For NC control, calculating the corrected sectional contour of a given body is a complex task requiring a great deal of calculation. Difficulties reside in defining a complex body and its surface and in calculating an equal distance for the cutter radius correction, taking possible collisions into account with a given accuracy. The amount of computer capacity and memory capacity needed is correspondingly high. To perform such calculations, additional hardware and software are necessary on the NC control computer. These include special arithmetic processors, for instance, as well as geometric methods and display methods for describing free-form surfaces.
It is known that relatively complex body contours can be constructed from simple contour parts such as circles and rectilinear lines. The tool radius corrections can be easily carried out with these simple contours. It becomes problematic, however, to ascertain the resultant tool path from the various corrected contours constructed to form the complex body since overlapping occurs when the various corrected contours are put together. Specifically, the tool path contours determined by the corrected path data do not necessarily coincide with the intersection lines of the assembled contour parts.
Accordingly, it is an object of the present invention to provide a method for simplifying the machining of curved intersection lines by bringing a tool path contour in close approximation to the curved contour.
A further object of the present invention is to provide a method of interpolating the curved contour taking into account the resolution of the machine.
A further object of the present invention is the elimination of the requirement of defining an incremental width, i.e. the length of an interpolation interval or a linearizing segment in advance and for the entire curve.
A still further object of the present invention is to provide a method of interpolating a curved contour intersection line so that only so many linearizing segments are made as are necessary so as not to exceed the maximum error. This results in linearizing segments closely approximating the curved contour while reducing the quantity of data and saving memory space. The interpolation may be conducted using 3-D rectilinear segments generated as a function of the actual curvature of the curved contour.